CPE

30,000 t/a Chlorinated Polyethylene (CPE) Process Scheme

1. Comparison of CPE Production Technologies
Currently, there are three main production methods for chlorinated polyethylene (CPE): the solution process, the suspension process, and the solid-phase process.
(1) Solution Process
This is the earliest method for p57roducing CPE. It was developed by the British company ICI in 1938. In this process, polyethylene (PE) is dissolved in halogenated hydrocarbons, followed by chlorine introduction to initiate the reaction, and finally the product is separated from the solution. There are two main variants: the low-temperature two-stage process and the high-temperature single-stage process, with carbon tetrachloride (CCl₄) being the most commonly used solvent. This process offers mild reaction conditions and mature operational procedures. The resulting CPE products can achieve chlorine contents ranging from 60% to 90%, with relatively uniform chlorine distribution, making it suitable for producing high-chlorine-content and high-crystallinity CPE grades.
However, the separation of CPE from the reaction solution and the removal of residual solvent from the product are complex operations, requiring high equipment costs. In addition, the solvent (CCl₄) is known to cause ozone layer depletion, leading to severe environmental concerns. This process is not suitable for large-scale production and is currently being phased out.
(2) Solid-Phase Process
In this process, chlorine gas or a mixture of chlorine and nitrogen is used as the chlorinating agent to chlorinate solid high-density polyethylene (HDPE), with quaternary ammonium salts employed as antistatic agents. The chlorination is first carried out at a temperature above 110℃, and then continued at 110–140℃until the required chlorine content is reached. Currently, the solid-phase process includes four reactor types: fluidized bed, fixed bed, rotary bed, and stirred bed. Industrial production mainly adopts the fluidized bed process.This process operates in the dry state, eliminating equipment corrosion and the issues of "three wastes" (wastewater, waste gas, and solid waste). The product is of high purity with low production costs. However, challenges remain in removing the heat of reaction, achieving uniform chlorine distribution in the chlorinated product, and scaling up the process—these issues have yet to be fully resolved and require further development and improvement.
(3) Suspension Process
Currently, the suspension process for CPE production includes two variants: the aqueous-phase suspension process and the acid-phase suspension process.
1) Aqueous-Phase Suspension Process
This process was first developed by Hoechst AG of Germany in 1960. Subsequently, it was also adopted by Osaka Soda Co., Ltd. and Showa Denko K.K. in Japan, Dow Chemical Company in the United States, as well as most domestic manufacturers in China.
In the aqueous-phase suspension process, water is used as the suspension medium. The raw materials are suspended in the aqueous phase with the aid of dispersants, emulsifiers, and initiators. A substitution reaction with chlorine gas is carried out at a controlled temperature until the required chlorine content is reached, at which point chlorine feeding is stopped to produce CPE. The hydrogen chloride generated during the reaction dissolves in water to form by-product hydrochloric acid (3-5%). Surface acid is removed from the material through water washing, while internal acid is neutralized by heating and caustic addition. After dewatering and drying, the CPE resin is obtained.This process is characterized by high water consumption, and the neutralized acidic wastewater is difficult to meet environmental discharge standards.
2) Acid-Phase Suspension Process
The acid-phase suspension process is an improved process based on the aqueous-phase suspension process. In this process, 17% hydrochloric acid is used as the suspension medium. The raw materials are suspended in the acid phase with the aid of additives, and react with chlorine gas at a controlled temperature. When the required chlorine content is reached, chlorine feeding is stopped, producing CPE. The hydrogen chloride generated during the reaction dissolves in the acid phase to form 25% high-concentration hydrochloric acid. A portion of this high-concentration acid is recycled for batch feeding, while the remainder is sold as a by-product. The material is then washed with water to remove acid, and subsequently dried in an intermittent FRP drying bed to obtain the CPE resin. Dilute acid is generated during the water washing step; part of it is used to prepare the acid medium for recycle feeding, and the rest is neutralized and discharged.A comparison of the two processes shows that the aqueous-phase process has a large discharge of dilute acidic wastewater (25 tons per ton of product), while the acid-phase process generates weak acidic wastewater (10 tons per ton of product) that is difficult to treat to meet discharge standards, with high treatment costs (RMB 100 / ton), resulting in significant environmental impact.
The combined acid-phase / aqueous-phase process for CPE production effectively addresses the technical challenges associated with wastewater treatment in the single aqueous-phase or acid-phase processes.
This combined process also resolves issues such as low automation, manual operation, high labor demand, and unstable operation in CPE production. At the same time, it complies with national regulations requiring that in production workshops (areas) involving nitration, hydrogenation, chlorination, fluorination, diazotization, peroxidation, and other reactions with a process hazard level of 3 or above, the number of operators on site at any given time shall not exceed three. Full-process automation control has been fully implemented in all key process stages, including batching, chlorination, deacidification, drying, pneumatic conveying, and mixing/packaging.
The combined acid-phase / aqueous-phase process is selected for CPE production.
Process Advantages of the Selected Process:
1)The process adopts advanced domestic technology that is mature and reliable, with low energy consumption, minimal pollution, high product quality, and full resource utilization, offering a significant competitive advantage. After technical renovation, the existing production plant can achieve safe, stable, and efficient operation.
2)The advanced technology and high level of equipment automation ensure stable product quality, safe and reliable operation, clean processing, environmental friendliness, and energy savings.
3)Full-process remote DCS (Distributed Control System) with mechanical interlock automation is adopted throughout the entire production process. Operators can monitor the operating status of all equipment in real time from the control room, and perform remote operations and adjustments, ensuring efficient and stable production.

2. Process Block Diagram

3. Material Balance Diagram

4. Raw Material and Utility Consumption

Table 4-1 Raw Material and Utility Consumption Quotas and Quantities

Table 4-2 Chemical Consumption Quotas and Quantities

Table 4-3 Auxiliary Material Consumption Quotas and Quantities

5. Product Specifications

6. Raw Material Specifications (HDPE)

7. Plant Layout
A. Batching, chlorination, neutralization and storage tank area: 80 m × 30 m
B. Drying area: 98.5 m × 32 m
C. Control room area: 30 m × 22 m
D. Warehouse and packaging area: 185 m × 30 m
E. Raw material storage area: 70 m × 38 m

8. Brief Process Description
(1) Acid Preparation
This unit is mainly for the blending of 25% concentrated acid and 5% dilute acid from the deacidification step. The 25% concentrated acid and 5% dilute acid from deacidification first enter the concentrated acid intermediate tank (R204) and the dilute acid intermediate tank (V004), respectively, for material recovery. They then pass through the existing closed-type filter presses (Y301A/B) to the concentrated acid collection tank (R205) and the dilute acid collection tank (V001), respectively. They are then pumped by the concentrated acid collection tank transfer pump (P0703) and the secondary acid transfer pump (P0803) to the primary acid tank (V304A/B) and the secondary acid tank (V305A/B) in the tank farm, respectively. The entire process is automatically controlled. The filter residue is sent to the filter residue dilution tank (V307), and then transferred by the filter residue transfer pump (P307) to the soaking kettles (R202-A3/A4).
The primary acid tank (V304A/B) and the secondary acid tank (V305A/B) are each equipped with flow meters at the discharge of the primary acid transfer pump (P304A/B) and the secondary acid transfer pump (P305A/B), respectively, to meter the required flow rates for blending hydrochloric acid to the process-required concentration.
The primary acid tank (V304A/B), secondary acid tank (V305A/B), and 18–19% acid preparation storage tank (V304C/D) are each provided with a concentration meter and a single suction valve.
(2) Raw Material Pneumatic Conveying and Feeding Section
This section includes raw material requisition, metering, bag breaking, feeding, and material conveying operations.
A set of automatic pneumatic feeding system (including Roots blower, surface cooler, bag breaker, etc.) is installed on the southeast side of the PVC warehouse, supplied as a complete package by the pneumatic conveying system manufacturer. The raw material ton bags supplied by the vendor are transported by forklift to the bag breaker. After bag breaking, the material is pneumatically conveyed to the raw material silo (V0204A/B). The raw material silo is interlocked with the weighing module of the metering hopper on the batching kettle (R207A/B), and the material is automatically conveyed by compressed air to the metering hopper above the batching kettle, where it is held for batching according to the process-specified weight.
(3) Batching
Start the agitator of the batching kettle (R203A/B) and start the 18–19% acid transfer pump (P306A/B). When the flow meter on the acid supply line reaches the set flow rate (normally 14 m³), the automatic control valve on the acid supply line and the 18–19% acid transfer pump are interlocked to shut off. Additives D17, GF10, and K30 are then added to the batching kettle. Open the vent valve of the batching kettle and open the bottom valve of the raw material metering hopper to feed the pre-weighed raw materials into the kettle through the screw conveyor, followed by mixing for 30 minutes. The batching kettle is equipped with a remote level transmitter, with level indication and alarm displayed in the main control room. The discharge valve of the batching kettle is remotely opened by the DCS. After discharging is completed, close the bottom valve of the batching kettle, add 3 m³of hydrochloric acid, mix, and transfer the slurry from the batching kettle to the corresponding chlorination reactor.
This unit consists of two batching kettles, each corresponding to six chlorination reactors.
(4) Chlorination
Liquid chlorine from the pipeline passes through the shut-off valve into the liquid chlorine distribution header and is then fed into each chlorination reactor under flow control.
In the suspended state, the substitution reaction between HDPE and chlorine takes place to produce CPE. The operation procedure is as follows: open the discharge valve of the batching kettle and the feed valve of the chlorination reactor, open the vent valve from the chlorination reactor (R201A1–B6) to the chlorination tail gas buffer tank, start the agitator of the reactor (AR201A1–B6), and open the automatic control valve (HV-08A–L) on the chlorination reactor feed line. The material from the batching kettle is transferred to the chlorination reactor by compressed air. After the batching kettle is emptied, close the feed valve of the chlorination reactor. Hydrochloric acid from the acid preparation header is added to the chlorination reactor through the automatic control valve (HA-06A/B). The vent valve of the chlorination reactor is kept open, as dissolved oxygen in the reactor needs to be gradually released as the temperature rises during the later stage. The jacket steam heating system of the chlorination reactor is started with one-click operation. The jacket temperature is automatically controlled by adding steam and circulating water to raise the reactor temperature to the initial reaction temperature, typically 70℃.The vent valve from the chlorination reactor to the chlorination tail gas system is then automatically closed. The liquid chlorine flow control valve (FV111A–L) is opened to introduce liquid chlorine into the reactor, and the instantaneous chlorine flow rate is automatically regulated. The chlorine feed rate is generally controlled at 1,000–1,500 kg/h, and the pressure is controlled at approximately 0.35 MPa, allowing a gradual increase in reactor pressure and temperature. During the reaction, the temperature is controlled at 128–130℃ until chlorine feeding is completed. The entire process is fully automatically controlled based on the set parameters.
After chlorine feeding is completed, the jacket cooling water inlet and outlet valves are automatically opened to cool the reactor contents until the material temperature drops to 80℃. The material slurry is then transferred to the receiving kettle by pressure. After pressure transfer is completed, the reactor is purged with compressed air for 15 minutes. The manhole cover of the reactor is opened to inspect the inner wall, agitator shaft, and baffles for any adhering material. If adhering material is found, the reactor is flushed with a high-pressure water gun.
During normal production, the two batching kettles can supply the feeding process for two reactors, and two reactors can be in the chlorination reaction state simultaneously.
The chemical reaction equation for HDPE chlorination to produce CPE with by-product hydrochloric acid is as follows:

[-CH₂-CH₂-CH₂-CH₂-]n+nCl₂→[-CH₂-CHCl-CH₂-CH₂-]n+nHCl

There are a total of 12 chlorination reactors in one production line. The production can be switched to produce different grades and products, and the chlorination reaction control conditions vary depending on the product grade.
(5) Transfer to Receiving Kettle
Start the receiving kettle transfer pump (P0601A/B). The DCS remotely opens the compressed air valve of the chlorination reactor (HV-203A～L), opens the discharge valve of the chlorination reactor (HV-09A～L), and opens the feed valve of the receiving kettle (HV-13/14/15AB) to transfer the material by compressed air to the receiving kettle (R202A1/A2). The receiving kettle is equipped with a level indicator. At the same time, the cooling water valves of the receiving kettle (HV-17A/B and HV-18A/B) are opened for cooling. After the reactor transfer is completed, an additional 2 m³of concentrated hydrochloric acid is added to rinse the reactor, and the rinse is also transferred to the receiving kettle.
(6) Concentrated Acid Removal and Soaking
Start the flat plate filter (C251), open the bottom discharge valve of the receiving kettle (HV-19A/B), and start the receiving kettle transfer pump (P0601A/B) to deliver the material from the receiving kettle to the flat plate filter. Adjust the slurry flow rate from the receiving kettle to filter the material slowly. (The filter is fully enclosed and equipped with a vacuum system. The hydrogen chloride gas extracted is scrubbed with water and then sent to the workshop fugitive emission absorption system for discharge in compliance with emission standards.) The separated 25% hydrochloric acid goes to the concentrated acid intermediate tank (R204), and then passes through the closed-type filter press and filter residue transfer pump to send the filter residue slurry to the soaking kettle (R202A3/A4). The concentrated acid intermediate tank is equipped with a remote level transmitter with high and low level alarms. The low-low level is interlocked to stop the concentrated acid intermediate tank transfer pump (P0702). The concentrated acid from the closed-type filter press enters the concentrated acid collection tank (R205), and is then transferred by the concentrated acid collection tank transfer pump (P0703) to the primary acid tank in the tank farm. The concentrated acid collection tank is equipped with a remote level transmitter with high and low level alarms. The low-low level is interlocked to stop the concentrated acid collection tank transfer pump (P0703). Neutralized water from the mother liquor tank in the tank farm is used as rinse water for the flat plate filter, with automatic control by a shut-off valve on the pipeline; field operators only need to perform routine inspections. An automatic control valve (HV-24A/B) is provided on the discharge line of the flat plate filter to send the material to the soaking kettle (R202-A3/A4). After the soaking kettle is charged, the material is thoroughly soaked and agitated to allow complete release of acid from the particles. The soaking kettle has a level indicator with a high level alarm. After one batch is filtered by the flat plate filter, the material is agitated for approximately one hour.
The 25% hydrochloric acid in the primary acid tank (V304A/B) in the tank farm is sent by the primary acid transfer pump (P304A/B) to the 18–19% acid preparation storage tank (V304C/D) for acid preparation. 
(7) Dilute Acid Removal and Intermediate Transfer
After the material in the soaking kettle has been soaked, open the bottom discharge automatic control valve of the soaking kettle (HV-25A/B), start the soaking kettle transfer pump (P0701A/B), start the dilute acid screw centrifuge (C261A/B), and open the feed control valve of the dilute acid screw centrifuge (HV-28A/B) to control the centrifuge feed rate. The centrifuged material is rinsed with mother liquor water (neutralized water) to the intermediate transfer kettle (R202-A5/A6).
The dilute hydrochloric acid enters the dilute acid intermediate tank V004, which is equipped with level indication and alarms, and automatically interlocked with the start/stop of the dilute acid intermediate transfer pump based on the level. The dilute hydrochloric acid is pumped to the closed-type filter press for filtration. The filtered dilute acid enters the dilute acid collection tank V001, which is equipped with level indication and alarms, and is automatically interlocked to stop the secondary acid transfer pump P0803 upon low-low level, sending the dilute acid to the secondary acid tank in the tank farm.The intermediate transfer kettle R202-A5/A6 receives the rinse slurry from the centrifuge. The level is transmitted remotely to the control room with alarms. After one batch is received, open the bottom switch valve HA-31A/B, start the intermediate transfer kettle transfer pump P0801A/B, and transfer the material to the neutralization reactor R202-B1～B5.
(8) Caustic Neutralization
The neutralization reactors R202-B1～B5 open the feed valves HV-33A–E/34/35/50 to receive material from the intermediate transfer kettle, and start the agitators. Open the heating valves HV-51A–E on the steam line to raise the temperature to 80℃, then add 15% caustic soda solution to start neutralization. The pH value in the neutralization reactor is controlled, with the pH meter interlocked with the caustic control valve PHV-01A～E. The valve is automatically closed when pH exceeds 10, and opened when pH drops below 7, until neutralization is complete. The neutralization reactor jacket is equipped with circulating cooling water for cooling, with automatic control valves HV-40A～E/HV-41A～E on the cooling water circulation line. Automatic control valves HV-42A～E are provided on the jacket steam condensate line, and the steam condensate is collected and sent to the circulating water tank. A demineralized water flushing line is provided on the neutralization reactor discharge line, with automatic control valve HV-56.
The caustic neutralization process releases the acid trapped within the material particles by heating, and neutralizes it with caustic soda solution. Since the amount of hydrochloric acid is very small, the heat of reaction is minimal, and there is essentially no temperature rise during the neutralization process. The caustic neutralization reactors are equipped with jacket circulating water cooling, with a high circulating return water temperature alarm loop TIA-01A～E. In the event of cooling system failure, the alarm alerts operators for response.
(9) De-alkalization
The neutralization reactor opens the discharge valve HV-36A–E, and the de-alkalization reactor R202-B6/B7 opens the feed valve HV-43A/B to receive material. After one batch is received, the valves are closed. Open the mother liquor water valve HV-47A/B of the de-alkalization reactor to drain the water. The mother liquor enters the de-alkalization water intermediate tank V003, which is equipped with level indication and high/low level alarms. The low-low level is interlocked to stop the de-alkalization water intermediate transfer pump P1002A/B and simultaneously interlocked to close the automatic control valve XV-06A/B on the pump discharge line. The control room opens the valve to send the de-alkalization water to the mother liquor tank in the tank farm. An automatic control valve HV-44A/B is provided on the industrial water feed line to the de-alkalization reactor. When the de-alkalization reactor is cooled by jacket circulating cooling water to 40℃, open the de-alkalization reactor discharge valve HV-48A/B. The material from the de-alkalization reactor enters the de-alkalization intermediate tank V002, which is equipped with level indication and high/low level alarms. The slurry is then pumped by the de-alkalization intermediate tank transfer pump P1001A/B to the mixing tank V501A/B/C. Process control conditions: caustic neutralization time 5–6 hours, operating cycle: 6 hours.
CPE neutralization reaction equation:

NaOH + HCl → NaCl+ H2O

(10) Treatment of Chlorine-Containing Tail Gas
The off-gases from the flat plate filter, dilute acid centrifuge, batching kettle, and receiving and cooling reactor enter the existing tail gas treatment unit of the plant. The tail gas treatment facilities are reused from the original system.
Remote temperature transmitters with alarms are installed on the discharge lines of the primary absorption heat exchanger E401 and the secondary absorption heat exchanger E402.
A chlorine toxic gas alarm is installed at the tail gas fan discharge.
NaOH concentration analyzers DT1702/1702 are installed on the discharge lines of the primary absorption circulation tank V401A/B and the secondary absorption circulation tank V402A/B, with high alarm at 20% concentration and low alarm at 5% concentration.
The waste sodium hypochlorite solution generated from the tail gas absorption tower is sent by the primary absorption circulation pump or the secondary absorption circulation pump to the wastewater treatment unit for disposal.

9. Equipment List

10. Waste Discharge Standards
A. Waste Acid Discharge: 25% hydrochloric acid, 12.26 t/h
Option 1: Deep desorption — hydrogen chloride is used for VCM production, while the remaining 1% hydrochloric acid is sent to the chlorination reaction batching system.
Note: 1.23 tons of steam is consumed per ton of 25% hydrochloric acid.
Option 2: Concentration to 31% hydrochloric acid for sale as a product.
B. Centrifuge Mother Liquor Discharge: 430 t/d
Option 1: Sent to secondary wastewater treatment after neutralization.
Option 2: Sent to the caustic soda primary brine dissolving system after organic removal.
C. Tail Gas Absorption Tower Discharge: Q = 50 Nm³/h, chlorine content in tail gas: 1 ppm
D. Drying Tail Gas Discharge: Q = 20,000 Nm³/h, dust content in tail gas: 20 ppm